This invention relates to a dry etching method used for applying etching to a metal film stacked on a semiconductor substrate to form a metal wiring layer, etc.
An arrangement used for a conventional dry etching method is shown in cross section in FIG. 1. A gas inlet 2 is formed in the upper surface of a reaction chamber 1 and an exhaust opening 3 is formed in the side surface of the reaction chamber 1. A metal plate or a semiconductor substrate on which a metal film is formed serving as a material 4 subject to etching is set within the reaction chamber 1. The exhaust opening 3 is connected to a decompressor (not shown) such as a vacuum pump. Thus, the interior of the reaction chamber 1 is in a decompressed condition. For a reactive gas for etching, a gas containing, as the main component, a halogen, e.g., fluorine, chlorine, bromine, or the like is used. Such a gas is introduced from the gas inlet 2 into the reaction chamber 1. Thus, etching is carried out. The reason why halogen is used is that chemical reaction force is large and vapor pressure of reaction product produced by etching is high, thus being easy to remove. This reactive gas is introduced into the reaction chamber 1 with it being raw, or in a plasma state. On the other hand, for the material 4 to be etched, as shown in FIG. 2, a metal layer 6 of, e.g., aluminum is stacked on a foundation 7 such as a base plate or substrate. On the metal layer 6, a resist 5 serving as a masking agent is coated. The reactive gas introduced into the reaction chamber 1 reacts with the metal layer 6 in the form of raw gas 8, ion 9 or radical 10 to form a reaction product 11. The reaction product 11 thus produced is exhausted from the exhaust opening 3.
However, where the vapor pressure of the reaction product 11 is low, such a product is difficult to exhaust, so that it stays within the reaction chamber 1, thus damaging etching. Particularly, where the material 4 to be etched is a metal alloy including a transition metal such as copper, the vapor pressure of the reaction product thereof is low. Thus, not only etching is damaged, but also etching residue is produced, resulting in the problem that the target pattern cannot be formed. For example, when etching is applied to Al-Si alloy using chlorine gas, the etching speed is 6000 .ANG./min. If copper is included therein, copper remains as a residue with it not being subjected to etching.
As just described above, where the material to be etched is a metal alloy containing transition metal, there is the problem that dry etching is not smoothly carried out.